Feb 292016
 

12 volt Power Supply using 7805

This 12 volt power supply using 7805 circuit is simple and useful. Sometimes we need to get 12 VDC, but we only have 5 or 9 volts regulators (7805, 7809).

This voltage regulator looks like fixed regulators we already know but with the difference that this has two additional resistors (180 and 120 ohms) (see the diagram).

These two resistors are used to establish a voltage divider, which puts a non zero voltaje on the COMMON pin of the 7805 regulator.

Calculating the voltage on the COMMON pin (now ADJ) of 7805, we get 7.2 volts. There are 7.2 volts across the 180 ohm resistor and 4.8 volts across the 120 ohm resistor.

12 volt power supply using 7805 regulator

From the above it follows that the 180 ohm resistor serves to increase the voltage at the COMMON pin. If we want to get a different voltage, we just have to change the value of the resistors.

Notes:

  • We change the name of the 7805 COMMON pin by the name ADJ because, the voltage on this pin can be changed using external resistors.
  • The voltage between the pin and the pin ADJ Out regulator, must be maintained at 5 volts (4.8 volts in our case).

List of components for 12 volt power supply using 7805 circuit

  • 1  diode bridge (DB)
  • 1  7805 voltage regulator IC
  • 1  120 ohms resistor (R1)
  • 1  180 ohms resistor (R2)
  • 1  220 ohms resistor (R3)
  • 1  2200 uF electrolytic capacitor (C1)
  • 1  10 uF electrolytic capacitor (C2)
  • 1  red LED (D)
  • 1 transformer 220/110VAC to 16VAC (not shown on the diagram) to be connected to the diode bridge
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